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Dye stuff industries produces a bulk quantity of waste which is disposed off into lakes and streams without any prior treatment and which has a significant negative impact on mankind and aquatic habitat also. Researchers were employing various treatment methodologies for the removal of the organic and inorganic waste. Research is going on to develop a low cost adsorbent which could be used for removing different sorts of dyes stuff which is discharged from the industrial effluent outlet. In this study, removal of Alizarin Red S Dye by sorption on Ca(OH)2 treated fly ash powder as an adsorbent. Investigating parameters employed in this study such as adsorbent dosage, pH, agitation speed. Adsorption is followed by Langmuir Isotherm and the adsorption behaviour is ascribed by Pseudo -second order kinetics.
Environmental Pollution has increased due to the dynamic usage of the dye consumed in the textile industry .Different sorts of dyes were used and without prior treatment they were disposed off into the lakes, streams and water bodies .These Dyes were not only create pollution for the aquatic fauna and flora, it has a significant negative impact on mankind also. More than 10,000 various kinds of dyes are commercially available which finds its use in many industrial processes such as textile, paper and plastics, leather, pharmaceutical, food, etc [2-4]. Under aerobic conditions, many dyes can decompose into carcinogenic aromatic amines which can be a cause serious health hazards to humans and animals [7, 8]. Moreover, dyes cause allergy, dermatitis, skin irritation and even cancers in humans .
Alizarin Red S (ARS) C14H6Na2O7S(Sodium Alizarin Sulphonate3,4-Dihydroxy-9,10-dioxo-2-anthraquininonesulfonic acid sodium salt C.I No: 58005) is a anthroquinone derived dye and the sodium salt is obtained by direct sulphonation of alizarin ,which finds its application in histochemical staining and various other applications [Ref- 23]
ARS were used to mark Japanese flounder [Ref IMP 1] etc. The dye is also used as an antidepressant drug and various pharmaceutical formulations [Ref IMP 2], It is also applied in employed as an electrochemical indicator for the recognition of saccharide , in the field of drug delivery also it has some potent application. For the detection of hydroxlylamine or copper .[20-22] Hoyte deciphered that the dye is toxic and assured that the normal growth may be affected .Baume and Derichsweiler employed intraperitoneal injections of a 2 percent the said dye , proved fatal to monkeys.[ref-35].It is also used in diagnosis of vascular calcification[ref42]
Adsorption or Biosorption could be probable alternative for the recent development in the waste water treatment research and application .This employs a wide application and advantages rather than the conventional techniques which are currently available. Low Cost Technology is an urgent need for the sustainability of the process. Industrial Waste and agricultural waste could be an alternative source of sorbent by means of which we could remediate the problem.
The main components of fly ash, a pozzolanic material are silicon dioxide, alumina, and iron oxide. Fly ash is the by-product of coal fired power plants and its use as the base material for the adsorption study is an attractive solution to both economical and environmental aspect . To have a better adsorbing capacity the sorbent must have a large specific surface area and good pore structure, thus to increase the adsorption capacity of fly ash it is hydrated with calcium hydroxide . It is also observed that with the increase in the alkalinity of fly ash, greater amount of harmful gases like SO2 and CO2 can be trapped [20-22]. The influence of various physico-chemical parameters such as adsorbent dose, initial solution pH and agitation speed of solution on Alizarin Red S adsorption was studied by batch adsorption studies. The most widely used adsorption isotherm models like Langmuir, and Freundlich were employed to study the equilibrium data. Kinetics of the adsorption process was examined by fitting the experimentally obtained equilibrium data with the kinetic models, viz. pseudo first order, pseudo-second-order.
Materials & Methods
The fly ash used for the experiment was first obtained from a coal based power plant from Durgapur, West Bengal, India. It was washed repeatedly with double distilled water to remove all dust and soluble impurities, which was then followed by drying at 343K for 24h. the dried fly ash was the suspended in 10% calcium Hydroxide (Ca(OH)2 solution and the suspension was autoclaved at 10 psi for 15min and incubated it for 3 hrs. The alkali solution was filtered off after the pre-treatment and the fly ash was washed until the pH of the wash was close to neutral. The treated fly ash was then dried at 343K for 24h. After drying, the adsorbent was used in all experiments.(Ref- MG FA)
Preparation of Adsorbate Solutions
Alizarin Red S (ARS) used in this study was of commercial grade (CI: 58005,MF: C14H6Na2O7S ,MW:364.24 Î»max :594nm ) was used without further purification . Fresh stock solution (500 mgL-1) was prepared by dissolving accurately weight quantity of the said dye in double -distilled water. An experimental dye solution of different concentration was prepared by diluting the stock solutions with desired volume of double- distilled water .The initial solution of the pH was adjusted with 0.1 M HCl and 0.1 M NaOH solutions by using a digital pH Metre (Eutech Instruments, Singapore).
The batch experiments were carried out in 250 ml glass stoppered, Erlenmeyer flasks with a working volume of 100ml, with an initial concentration of 50 mgL-1. A fixed amount of adsorbent was added to the solution. The flasks were agitated at a constant speed of 140 rpm for 240 minutes(4hrs) in an incubator shaker ( Model Innova 42, New Brunswick Scientific, Canada) at 303Â±1 K. The influence of various process parameters like pH (2.0,4.0,6.0,8.0,10.0),adsorbent dosage (0.5, 1, 2, 3, 4 gL-1) and Agitation Speed (100,140,180,220 rpm) were calculated during the current study. To study the residual dye concentration in the solution, samples were taken out from the flask at predetermined time intervals. The remaining dye concentration in each flask after a specified time of the experiment was analysed by using UV-Vis spectrophotometer (Tech Comp UV2310 Spectrophotometer). The amount of dye adsorbed per unit adsorbent (mg dye per g adsorbent) was calculated according the mass balance on the dye concentration using Eqn.(1):
Now for calculating the percentage removal (%) of dye from the solution the following equation can be used.
Results and discussion
Effect of pH:
The initial solution pH is a significant operating parameter Fig. 1 shows the effect of the pH on the adsorption of ARS on adsorbent. The dye uptake was decreased as the pH of the solution increased. The decrease in the uptake values at low pH i.e. at pH 3 was attributed due to the decrease in ARS dissociation which led to lower concentration of anionic dyes .This could be explained on the basis of the lower extent of protonation of amino groups at high pH. ARS was first dissolved and the sulfonate groups of AR dissociate and were converted into anionic dye ions. Under acidic conditions sulfonate groups combined with H+ which decreased the adsorption capacity of ARS. So, in acidic conditions ARS gives best removal .Similar trend of result also observed by [ref-imp4] and [28 no ref of the imp 4 paper]
Effect of adsorbent dosage:
Biosorbent dose is also an influencing operating parameter. The influence of adsorbent dosage on ARS sorption by TFA was studied in the range of 0.5- 4 g. The percentage of removal of dye increased from 90 % to 97 % .Fig 1 elucidates that when the dose increased from 0.5 to 1 g the removal percentage is maximum and when the dose is increase up to 4 g. there is no significant removal is observed from the obtained data. This could be more number of active sites present in the adsorbent and saturation could be due to the aggregation which would lead to decrease in total surface area of the adsorbent and increase in diffusional path length .Therefore, in the following experiment, adsorbent dose was fixed at 1 g(Carbohydrate polymers).These type of observation was also put forwarded by some researchers earlier.
FIG 2 .Effect of Adsorbent Dose.
Effect of agitation Speed:
Agitation speed was also studied in this present work during adsorption the agitation speed was varied from 100 rpm to 220 rpm using predetermined quantity (1gm)of Treated fly ash and fixed amount of ARS solution of 50mgL-1 in an Incubator shaker ModelInnova42, New Brunswick Scientific, Canada).The initial and final concentrations were measure using UV/Vis Spectrophotometer ,Model TechCompUV2310) .Fig 2 shows that at higher agitation dye removal dye percent decrease due to the high centrifugal force which results in loosely bound dye material is desorbed form the Treated Fly ash surface the percentage of sorption decreased from 94.55% to 75% . Similar trend was observed by (Saha et al -MB FA)
Fig 3.Effect of Agitation Speed
In the present study, the Langmuir, and Freundlich isotherm models were used to explain the equilibrium of the biosorption data obtained from the experiment .The Langmuir assumption justifies the monolayer adsorption of the homogeneous surface of the adsorbent. The equilibrium relationship between the adsorbate and adsorbent is explained by the adsorption isotherm. [23,26] .The Langmuir sorption isotherm elucidates that the uptake occurs on a homogeneous surface by monolayer sorption without interaction between adsorbed molecules and is commonly expressed
Where qe (mgg-1) and Ce (mgL-1) are the solid phase and liquid phase concentration of the adsorbate at equilibrium respectively ,qm (mgg-1 ) is the maximum adsorption capacity , and KL (Lg-1) is the adsorption equilibrium constant . The constants KL and qm can be determined from the slope and intercept of the plot between Ce /Qe and Ce.
The Freundlich isotherm is applicable to non ideal adsorption on heterogeneous surfaces and the linear form of the isotherm can be represented as:
where qe is the equilibrium dye concentration on adsorbent (mg gâˆ’1), Ce is the equilibrium dye concentration in solution (mg Lâˆ’1), KF (mg gâˆ’1) (Lgâˆ’1)1/n is the Freundlich constant related to sorption capacity and n is the heterogeneity factor. KF and 1/n are calculated from the intercept and slope of the straight line of the plot log qe versus log Ce.
The Langmuir and Freundlich Isotherm were employed for the sorption of ARS onto Ca(OH)2 modified Fly Ash at 30Â°C are represented in Fig 4 and 5.The Langmuir and Freundlich constants calculated from the isotherm at 30Â°C with the correlation coefficients is presented in Table 1.From the Table 1 data Langmuir model fits well with experimental data of the ARS removal by Ca(OH)2 treated fly ash. The Langmuir Isotherm explains that the sorption is monolayer and homogeneous distribution of the active sites on biosorbent surface area.
Fig : Langmuir Isotherm curve Fig : Freundlich Isotherm Curve
To decipher the kinetics of the adsorption process, the pseudo first order (27,28),pseudo - second order (27,29), were employed. Pseudo first order equation is represented below:
Pseudo -Second Order Kinetic Model
The linear form of Pseudo second order kinetic model can be expresses as follows
The kinetic data fitted well with the pseudo second order kinetic equation. The experimental values showed linearity and R2 >0.999.The best correlation provided by the pseudo second order suggests that chemical sorption involving forces or sharing of electrons between adsorbent and adsorbate might be a significant.
Fig : Pseudo -Second Order
The present study indicates the application of alkali treated fly ash as a potent adsorbent for the removal of wastes which is bearing with ARS .The sorption was governed by low pH and it is found that at pH3 is best suited for conducting all experiments. The adsorption isotherms best fitted with Langmuir at all temperatures. The adsorption data gives good agreement with the pseudo-second order kinetic model. The results confirmed that the low cost easy available fly ash may be an effective for the treatment of effluent and dyestuff industries.